


Behind Closed Doors

by PsychoMeows



Series: Multiverse Sansby [1]
Category: Undertale (Video Game)
Genre: Aftercare, Alternate Universe - Underfell (Undertale), Anal Fingering, Begging, Choking, Dom/sub, Ecto-Genitalia (Undertale), Ecto-Vagina (Undertale), Established Relationship, Forbidden Love, Insults, Laughter During Sex, Love, M/M, Overstimulation, Painful Sex, Plot What Plot/Porn Without Plot, Rough Sex, Secret love, Sexual Roleplay, Spanking, Sub Sans (Undertale), Teasing, Vaginal Fingering, Vaginal Sex, Violent Sex, dom grillby
Language: English
Status: Completed
Published: 2020-04-21
Updated: 2020-04-21
Packaged: 2021-03-02 04:55:00
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 4,861
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/23769595
Author URL: https://archiveofourown.org/users/PsychoMeows/pseuds/PsychoMeows
Summary: Underfell isn't a nice place but Sans and Grillby find a way to make it work. They can't be loving out in the open but behind closed doors they can do what they want. They can be rough or they can be loving and no one can judge them for it.(I'm a dirty sinner for writing this...)
Relationships: Grillby/Sans, Sansby
Series: Multiverse Sansby [1]
Series URL: https://archiveofourown.org/series/1720648
Comments: 1
Kudos: 73





	Behind Closed Doors

The glass hit the bar top hard, making a loud thunk sound. Sans's face soon followed, making a louder thunk. No one payed much attention to him. They were either too shitfaced, busy or, most likely, uncaring to bother with the little skeleton. All except one person.

Grillby looked over to Sans and sighed. He wasn't about to go over and help the drunken skeleton; he didn't want anyone to think he cared about the runt. If they did start to think that, then Sans would be a bigger target than he already was. After all kidnapping or killing him would get to both the Lieutenant of the Royal Guard and the notorious bartender, who had a lot of power in Snowdin, with both his legal and illegal businesses. He had a good thing going in Snowdin and he wasn't about to ruin it by doing something as simple as helping Sans's drunken ass home.

If he was seen going over to Sans right now, he'd have to beat his ass for once again not having the money to pay his tab and kick him out. He wanted Sans to stay, after all if he was here, he wasn't getting beaten up by his dick of a brother. So Grillby quickly looked away from the skeleton and instead he went to throw out the drunken bunny who had passed out on the floor, after he went into her purse took all her money.

It wouldn't be long until closing, Grillby wondered if he'd be able to 'force' Sans upstairs again today. Fucking him in the bed was better than doing it at the bar after all; much more comfortable and he didn't have to worry as much about cleaning up.

Sans was snoring. That soothed the worries (that Grillby _totally_ didn't have) that the runt was alright and hadn't suddenly Fallen Down or anything. Although he was still (definitely not) worried about how drunk Sans was. It was just that a drunken partner made for bad sex, it wasn't like he was worried about him having alcohol poisoning or being too drunk to consent. Grillby always just took what he wanted, he didn't need Sans's consent to do whatever he pleased with him.

At least that was what Grillby told himself. He knew deep down he cared for Sans and if he ever said no or told him to stop then he would. Not like Sans had ever said no whenever Grillby decided to claim him, no matter how violent the method of said claiming.

Grillby went back to cleaning as he watched over his bar, ready to jump in to stop any fights from damaging his bar and to watch for anyone stupid enough to attempt to steal from him.

Slowly the bar began to quiet as customer began to leave. Sans's snoring got louder and the few remaining monsters that Grillby would probably have to throw out were shooting the little skeleton dirty looks.

"Yo, Grillby!" One decided to call out, "you gonna kick out the runt yet? He's real annoying."

Grillby scowled, "...The little fuck owes me a lot of money... I think a proper lesson is needed... So he's staying after closing." Grillby let himself heat up as he made a fist with his right hand and punched his left palm, signalling that Sans was about to get a real good beating. The kind of beating that would be really violent and best severed after closing.

The others scoffed and returned to their business. It wasn't long before they left, however. Either too annoyed by Sans's snoring or afraid the clearly angry fire elemental would violently remove them from his establishment.

Grillby smiled as he walked over and locked the door. He hoped none of them would alert Papyrus to his plan of beating the older brother. The Lieutenant could come over and ruin their fun claiming that Sans was his to beat or claiming he wished to take care of the punishment. Punishment wasn't Grillby's goal.

He walked back to the bar and saw that Sans was no longer face planting the table but had turned his head to the side. He was still fast asleep and looked almost peaceful. Grillby had a brief thought that he should find a sharpie and draw dicks on Sans's face but he quickly got rid of the immature idea as funny as it'd be. He did, however, wish to leave marks on the runt, just not pen or bruises.

He slapped Sans on the back causing him to jump awake. Sans looked around before he set his eyes on the bartender. "the fuck was that for!? asshole!" He snapped as he rubbed his sore spine.

"...You were sleeping... Had to wake you somehow."

"ya didn't have ta hit me!"

Grillby just shrugged and he sat on the stool beside him. "...You still owe me."

Sans rolled his eyes, "come on, man. you know i'm good for it... hey, what time is it? i should be getting home or boss'll be real mad."

Sans moved to stand but Grillby grabbed him by the hood and pulled him back down. He looked over the smaller monster who was clearly still a little drunk but that didn't bother him. Grillby grabbed Sans's left femur roughly and ran his hand down it. "...I'll give you a choice; on the bar and so hard you'll be limping for weeks or upstairs in my bed and I'll go easy on you... Slightly easier."

Sans scowled at him and rolled his eyes, "oh fuck you!"

Grillby raised a brow and chuckled. "...Yes... That's the plan... Other way around though."

Sans sighed and looked away from Grillby and over at the wall of booze that was behind the bar. "i need another drink."

Grillby's hand moved off of Sans's leg only to slip under his shirt and grab his spine in a vice like grip making the runt gasp. "...No, not until I've had my way with you."

Sans flinched and pulled Grillby's arm away from him and stood up. "yer a real dick, ya know that? i don't have time for this." He wanted it though, so badly but he had to keep up appearances even if they were alone it was hard to drop the act. Besides if Papyrus just so happened to break down the door, Sans had to look like he wasn't submitting so easily to the elemental. He dreaded to think what he'd do to them both if he found Sans willingly lying naked and spread under Grillby.

"...I disagree... I told the others that I was going to beat the shit out of you because of your tab... If Papyrus was going to interrupt he would've by now... Either they haven't told him or he doesn't give a fuck... So why don't you get upstairs or get on the bar?"

Knowing Papyrus probably wasn't going to interrupt put Sans at ease. He was about to do as he was told and head upstairs but a fun idea came to his mind. "why don't you?" Sans replied, a challenging look in his eyes.

"...Excuse me? ...Are you challenging me?" Grillby asked as he stood as well, drawing himself up to look bigger and looking down at the smaller monster.

Sans wasn't going to back down, he glared up at him. "hell yeah i am. why do you always get ta stick it in me?"

Grillby reached forward and grabbed Sans by the neck causing him to gasp. "...Because I'm a powerful elemental and you're just a runt." He squeezed Sans's neck hard before he let go and shoved him a little. "...Now strip and get on the bar... You don't get a choice now."

Sans narrowed his sockets. He wondered how far he could take this without Grillby losing interest, he wondered if he'd maybe actually be able to dominate him... That was unlikely but worth a shot. He lifted his left hand and reached around to roughly grope Grillby's ass as hard as he could. "how about no?" He said looking up and making eye contact, he wasn't going to back down easily.

The skeleton went flying when Grillby's fist connected with his jaw. He landed flat on his ass and looked up again at the bartender.

"that was uncalled for!"

Grillby huffed and offered Sans his hand. "...That's what you get for challenging me... Get up."

Sans looked at the hand and then back at Grillby before he looked down, acting submissive. He took the hand and was pulled up. Not wanting to give up so easily he kicked at Grillby aiming for his balls unfortunately Grillby was faster and he grabbed Sans's leg mid kick and threw him back on the floor.

"...Looks to me like you want me to fuck you on the floor?" There was a teasing tone to his voice that made Sans scowl.

"i fucking hate you!" He growled getting up again and getting in Grillby's face as well as he could with being so much shorter than the elemental. "i really fucking hate you. with every fibre of my soul i hate you!"

Sans was punched again not as hard this time and he only stumbled a little. Grillby once again grabbed Sans by the neck, dragged him over and threw him face first onto the bar, legs dangling over the side and his ass in the perfect position for Grillby to smack. He did just that, bringing his hand down hard and loving the sound Sans made. He was surprised to feel something there; so Sans was turned on by this, his ecto was formed. He spanked Sans as hard as he could about ten more times making him yelp slightly each time before he stopped and grabbed the waist band of his shorts and pulled them off. The red ecto ass was a little bit brighter in the areas where Grillby had smacked and he was happy to see that despite the attempt at dominance he had formed a pussy.

The elemental leaned over Sans pressing his clothed erection against Sans's ass. "...I hate you too," Grillby hissed, "...I hate you so much." He then brought his hand down on Sans's ass again much harder than before making Sans yell out.

"fucking prick!" Sans snapped, he was gripping the edge of the bar hard, his sharp claws making scratch marks on it. "i'm gonna get you back one day."

"...Keep telling yourself that, whore." Grillby backed up a little, he firmly pressed two fingers to Sans's clit and then dragged them down, roughly running them alone the length of his partner's slit before quickly jamming them inside making Sans moan. "...Even though you're complaining, you're real wet... Even summoned a pussy for me... I know you want this." Grillby certainly didn't go easy on the little skeleton as he roughly pulled out his fingers only to jam them right back in and curl them before he scissored them open.

Sans squirmed under the rough treatment as he held back his moans of pleasure, he refused to give the asshole the stratification of knowing just how good he was making him feel. He couldn't control his body however as he pushed back on Grillby's fingers, he wanted more.

"...Desperate little fucker, ain't ya?" Grillby said as his spanked the skeleton with his free hand as his other continued to violently finger fuck him.

"would ya shut the fuck up!?" Sans said only to scream when he felt another hard slap on his ass, "fuck! can ya at least ease up on the hitting!?"

Sans let out a sharp gasp as Grillby squeezed the part of his ass he just slapped and at the same time he harshly pulled out his fingers. "...But Sansy..." Sans shivered at the sickly sweet tone Grillby was using, so condescending. "...You need to be punished... You owe me a lot of money and you challenged me... Don't you think you deserve it?" He slapped Sans again although not as hard.

Sans scowled, he knew how to make Grillby stop; all he had to do was apologise but his pride wouldn't let him. Or he could use the safe word but then Grillby would stop everything and Sans didn't want to stop. Besides it was turning him on, not that he'd admit it. If it ever got out that Sans, older brother of the Great and Terrible Papyrus was a masochist that got turned on by being spanked, things would turn out badly for him and his brother. They'd be ridiculed and mocked, Papyrus would be humiliated and Sans could never do that to his bro no matter how much of an ass he was. Sans just settled on growling another, "fuck you!"

Grillby laughed as he took that as permission to continue and slapped Sans again this time turning up the heat to lightly burn Sans's ecto ass. Sans couldn't stop the moan this time and he quickly brought his hand up to cover his mouth. That only encouraged Grillby to keep going as he slapped him again and again.

Sans knew he should probably stop this now before he was too sore to sit down. He _really_ didn't want to have to explain to Papyrus why he couldn't sit, after all he was a lazy fuck who was always sitting on his ass. Papyrus would be suspicious and Sans didn't think he could think of a good enough lie and he wasn't about to tell him that it was because Grillby had spanked him before he fucked him.

He pulled his hand away from him mouth, trying his best not to whimper as he spoke up, "ok, ok! that's enough, 'm sorry!"

Sans gasped as Grillby stopped and instead shoved one finger into his asshole and then began to slowly move it in and out. "...What are you sorry for, Sans?"

Sans groaned, "really!?" He moaned loudly as Grillby added another finger to his ass thrusting them in and out roughly. "alright! 'm sorry for not paying my tab!"

Another finger was added, making Sans squirm as Grillby began to get rougher with his fingering, pressing up against something that made Sans feel so good. Having three fingers up his ass shouldn't feel so good but it did.

"...And?" Grillby said, Sans couldn't see him but he could tell the elemental was smirking at his current situation.

"and 'm sorry for trying to challenge you!"

"...Good boy," Grillby said as be thrust his fingers in his ass a couple more times before he quickly removed them. He grabbed the smaller monster by the hip and flipped him over so he was on his back. He then grabbed his femurs and spread then wide. His pussy was dripping wet and Grillby took his time admiring it, spreading it open and rubbing lightly over the clit, not firm enough to give Sans a lot of pleasure, just enough to tease him. "...Don't move," the elemental ordered and he backed away going behind the bar and pouring himself a glass of whisky.

He was hoping Sans would disobey so he could punish him a little more but it seemed he'd had enough. The skeleton stayed where he was, lying spread on the bar top looking at Grillby with a mix of hatred and lust. Grillby huffed and downed his drink not breaking eye contact, he then put down his glass and gently stroked Sans's skull. Sans leaned into the loving gesture and closed his eyes with a gentle smile on his face. That was all Grillby needed to know Sans still wanted this.

He walked back to the other side and unzipped his pants. He pulled his dick out and rubbed it a few times to give himself some relief before getting back between his partner's legs. He really just wanted to shove it in him, he'd taken longer than he'd planned to spank and tease Sans and he was at a point of desperation but he couldn't resist teasing the skeleton a little more. He rubbed the head of his dick on Sans's clit making the runt whine. He sure sounded desperate.

"come on, grillbz! just shove it in already!" Sans complained as he reached down to grab the hot fire cock and try to line it up but Grillby grabbed his hand and pulled it away.

"...You think you deserve it?"

Sans let out another groan. "come on man, don't make me beg!"

Grillby smirked, "...I want you to beg though... Of course you don't have to... I could just take you to my room, tie you up and leave you desperate and without stimulation while I take care of myself in front of you."

"fucking jerk!"

Grillby ran his cock over Sans's pussy and rubbed Sans's hip and then slowly moved his hand under Sans's shirt to rub at his spine. "...Well, what will it be, slut?"

Sans narrowed his eye sockets and said sarcastically, "oh, grillbz please fuck me! i need your tiny dick!" He could help but laugh at the end.

Grillby sighed and grabbed Sans's coat to pull him up. "...Alright then, time to tie you up."

Sans's eyes widened as he realised that threat had been serious. "no! wait! 'm sorry!" He protested. "yer dick ain't tiny! fuck... i mean that thing's huge!"

Grillby couldn't help but laugh and Sans joined in, Sans's sarcasm had killed the mood a little but he wasn't going to let it get in the way. He shoved him back down onto the bar. He took a second to control himself before he got back to it. "...Beg."

"please!" Sans compiled, still giggling a little but Grillby ignored it. "please grillby, i need it! please fuck me!"

Grillby lent over Sans to kiss him roughly before he pulled back and tightly grabbed Sans's hips and jerked him towards him as he thrust into him. Sans screamed out as he felt his pussy stretch to accommodate Grillby's length. The elemental never waited for Sans to adjust before he began his hard thrusting. Sans was tight as always and Grillby loved it. He closed his eyes tight as he moved his hips hard and fast, slamming into the smaller monster with force. He loved the sound of the wet slapping as they joined together and the breathless moans Sans made as he was fucked into the bar top. Grillby's grip on Sans's hips tightened as he went faster, moving Sans with him. His dick was so deep inside Sans and it all felt so good. He loved the feeling he got when Sans submitted to him like this. The tough foulmouthed skeleton was so vulnerable like this, he gave Grillby everything. In a position like this it wouldn't be hard for Grillby to dust him; he only had one HP and his defences were lowered... It'd be so easy, anyone else would've taken the opportunity, people would call him dumb for not taking the chance but Grillby would _never_ hurt him. He felt so happy that Sans trusted him enough to be so vulnerable with him and that fact _almost_ felt as good as his pussy squeezing his cock as he thrust.

Sans had stopped digging his claws into the bar and instead grabbed hold of Grillby's arms. He loved this, it always felt so good, no matter how hard Grillby fucked him. He'd be sore tomorrow but it was worth it. He let himself get lost in it. He could relax and let Grillby do what he wanted, he didn't have to worry about him deciding he wanted to dust him. Sans trusted Grillby, even if he was a total dickhead. He felt safe with him and could really enjoy himself here at Grillby's after closing with the bartender balls deep inside of him and thrusting into him hard.

They were both moaning in pleasure as the rough thrusting continued with no hint of slowing down or stopping. Grillby smiled down at his prey who was lying there with his mouth open and eyes shut. Still not slowing his thrusts Grillby lent over Sans again and lightly slapped him in the face causing Sans to open his eyes and glare up at him. "bastard," he managed to moan out, earning him another slap in the face. "fucking asshole, i hate you!"

Grillby grabbed hold of Sans's neck and squeezed making Sans choke but Grillby didn't let go. Sans was a skeleton, he didn't have lungs or airways so he could choke him all he wanted without risking his life. "...Insult me all you want... I know you're loving this... Just look at how wet you are... You're squeezing me so good." The elemental squeezed harder as he jerked his hips forward roughly and slapped Sans's hip with his other hand before reaching down to firmly rub his clit.

Sans moaned loudly, there was so much sensations from so many different places and he loved it. He lifted his head giving Grillby more of his neck letting him choke him better and he wrapped his legs around the elemental's waist. He was so close, just a little more.

He felt his eyes begin to close again but he fought it, he wanted to look at Grillby as he was fucked. He tired to speak, to let Grillby know he was about to cum but all that came out as a breathless moan. He could tap out and Grillby would stop choking him but then the flaming hot bartender would take that as a win and Sans refused to boast his ego. Instead he reached down with his left hand and pushed Grillby's fingers on his clit down firmer only for the elemental to slap his hand away and speed up again.

It was all too much and Sans's arched his back and grabbed onto the arm that was chocking him. His body shuddered with pleasure as he came, tightening around the cock that was inside him, his moan was loud and he continued to moan loudly as Grillby didn't stop.

The elemental let go of his throat letting Sans cough and breath heavily as he tried to regain control of his breathing. That was hard since he was being overstimulated as Grillby kept thrusting into him and rubbing his clit. It was almost painful but Sans found himself enjoying it.

"...I'm not done with you," Grillby said, "...I'm not going to stop until I cum."

Sans could only nod as he unwrapped his legs from around Grillby's waist and spread them as wide as they could go. Grillby went at it harder as he slapped Sans's hips and pushed hard at his clit. He was getting close now, it wouldn't last much longer.

Sans's vision was blurring and his eyes began to fill with tears. All he could make out was a beautiful purple light as he stared up. He was going to cum again, it hurt but he was going to cum again...

With a low growl Grillby came inside of Sans, his hot cum shooting right up into the runt making the little skeleton cum again as well. Sans let his head fall back and hit the table hard as he fainted from the over stimulation.

He wasn't out for long and when he came to he saw that Grillby had pulled out and was tucking himself back into his pants. Sans groaned as he sat up and felt some hot cum spill out onto the bar top.

"you're a fucking jerk," he said.

Grillby simply laughed and kissed Sans's cheek. "...Yeah, I am... But I'm _your_ jerk," he said pressing his forehead to his lover's, staring into his eyes, "...And you're _mine_... You belong to _me_."

Sans rolled his eyes and laughed, "yeah, yeah, mr overly possessive." He moved in to kiss Grillby before he pushed him away and grabbed a napkin to clean off all the cum from his bones. "did ya really have ta cum in me? such a mess... would it kill ya to wear a condom?"

Grillby laughed as he also grabbed a napkin and began to help Sans clean up. "...It feels better without one... Besides, do you know how much fireproof condoms cost?"

Sans shrugged and pulled his shorts back on. "ya could at least pull out though?"

The elemental rolled his eyes and replied sarcastically, "...Fine, next time I'll shove it in your mouth, choke you on it and cum down your throat."

They both laughed. Sans shook his head, "please don't, that sounds worse!"

Grillby nuzzled Sans's face and kissed him again before he got up and poured them both a glass of whisky. He raised his and Sans clanked their glasses before they both downed it.

Grillby then scooped Sans up and into his arms and began to carry him upstairs princess style. The skeleton relaxed into the hold, taking in his lover's warmth and smell. "i love ya," he muttered barely loud enough for the other to hear.

"... ... ...I love you too."

Sans hummed and closed his eyes as he let himself be carried up and placed on a soft bed. Grillby got in next to him and held him close, neither of them undressing since they wouldn't have long enough to sleep together; Papyrus would soon come looking for Sans.

"i really love you," Sans said again and he snuggled closer. "ya know i didn't mean anything i said back there."

"...I know... Same here... All of that's just dirty talk, it's hot... I love you so much." Grillby wrapped his arms around Sans and held him. "...I'd never actually hurt you."

Sans smiled, it was so rare to find such love in his universe. It made him jealous of his other selves in the nicer universes, they were free to show their affections for their Grillbys. He couldn't, it'd ruin Grillby's reputation and put Sans in more danger. He was just glad to have these little moments where there was nothing but their love, where he was free to relax and enjoy just being held.

"...I wish we could come out," Grillby whispered, thinking aloud. "...I wish I could just grab you and kiss you in front of everyone and let them know you're mine."

Sans couldn't help smile at that. "bad idea there, sweetheart."

"... ...I know."

Sans sighed and looked at his lover who was looking sweetly back at him. "sometimes i think about telling paps. he'd probably beat the shit outta me and then challenge you to a fight... i'd probably be yer prize if ya won."

Grillby laughed, "...Shouldn't it be the job of an older sibling or the father to fight their family member's lover?"

Sans laughed, "well, paps may be younger than me but he is stronger and feels it's his job to protect me, no matter how fucked up he does said 'protecting'... besides i don't have an older sibling and my bastard of a father is long dead. he probably wouldn't give a shit about who was fucking me anyway. he probably would've just made ya pay for me."

Grillby raised a brow, Sans had never talked about his father before and the bartender would be lying if he said he wasn't curious about him. "...Abusive?" He asked, he knew it was very common for parents to abuse their children. Whether it was to make them stronger or to seem like they didn't care so their kids wouldn't be used as pawns against them.

Sans snorted, "that's putting it lightly. we were hardly even his kids. to him we were just lab rats ta be experimented on and tortured for fun. he was totally nuts. when we stopped being useful to him he was goin' ta kill us. got real close ta stabbing me with a lethal injection. then he decided at the last second that he'd rather profit from us and told us he'd sell us separately as slaves to the highest bidders."

Grillby was frowning at Sans, he gently stocked his lover's face and kissed his forehead. "...That's really fucked up."

Sans nodded, "yeah, luckily for us paps managed grab the keys off of him then paps unlocked our cells. i then sabotaged his experiment and it resulted him shattering across space and time. he ain't coming back."

"...Good, anyone who does shit like that to kids deserves it... Even the King isn't that fucked up."

Sans hummed in agreement and brought his arms up to hug Grillby. "i'm happy with how my life turned out. it could be better but hey nothing can be truly perfect in this universe. i'm lucky to have you."

They smiled at each other, settling into a comfortable silence. The peace wouldn't last long but they were both happy to have any time they could get to be like this with each other. Once Papyrus called they'd have to part for the day and act like jerks to each other again but they looked forward to the next time they got the chance to be alone together behind closed doors.

**Author's Note:**

> So as you can tell I really like Sansby lol. I have a few more Sansby fics in the works so expect more of this ship from me.


End file.
